Web tension measuring devices



Aug. 24, 1965 s. WILLIAMS WEB TENSION MEASURING DEVICES Filed May .24,1962 WEB TENSION MEASURING DEVICES Kenneth Sydney Williams, Bridgwater,Somerset, England, assignor to British Cellophane Limited, Bridgwater,Somerset, England, a British company Filed May 24, 1962, Ser. No.197,426 Claims priority, application Great Britain, June 7, 1961,

20,600/61 4-Claims. (Cl. 73-143) 7 This invention relates to web tensionmeasuring devices.

In aknown device for measuring the tension in a stationary or travellingweb stretched between two spaced supports, a movable membenfor'example aroller mounted at the end of a pivoted arm, is urged by weights orspring pressure against the web. At equilibrium, when the resistanceolfered by the web balances the force ap plied to the member, the.position of the member with respect to a fixed datum point is a measureof the web tension. Such a device, however, requires the provision ofvmoving mechanical linkage and; accommodation for springs or weights andis a cumbersome mechanism to incorporate in Web-handling machinery.Further, since positive contact by the member with the web is anessential feature of the operation of the device, it cannot readily beused with fragile webs or webs that are wet with ink or coatingcompositions.

The object of the present invention is to provide an improved webtension measuring device in which the tension of a web canbe measuredwithout contacting the web with a solid surface.

Accordingly, the present invention includes an apparatus for measuringthe tension in a web which apparatus comprises an arcuate surface aroundwhich the web is passed, the arcuate surface having apertures throughwhich a gaseous medium can be supplied under pressure to provide asupporting gaseous cushion between the under surface of the web and thearcuate surface, a supply means for continuously supplying the gaseousmedium under pressure to the apertures and one or more pressuremeasuring devices for determining the pressure of the gaseous medium inthe gaseous cushion at one or more selected points.

The arcuate surface should have sufiicient surface area to permit of achange in direction of the Web through an angle of at least 40 and up to180 as it passes round the arcuate surface and the apertures arepreferably arranged in two or more rows in a direction transverse to thepath of the web.

In a peferred form of the apparatus, face is provided by a tubularmember having a series of holes drilled through the tube wall in thearea of the surface over which the web passes and gaseous medium, forexample air, is supplied under pressure to the interior of the tube.

It is an essential feature of the invention that the web is entirelysupported by the gaseous cushion as it passes round the arcuate surface.Under these circumstances, the pressure of gaseous medium (P) at a pointin the gaseous cushion may, for practical purposes be related to thetension per unit width (T) in the web immediately above the point ofpressure determination by the expression the arcuate surwhere R is theradius of the arcuate surface.

A convenient method of determining the pressure of the gaseous medium ata selected point in the gaseous cushion is to provide a hole in thearcuate surface at a. convenient point beneath the web and connect thehole United States Patent by means of a pipe to a manometer or otherconventional pressure measuring or indicating device when the pressurerecorded will be a measure of the tension in the web immediately abovethe hole.

The apparatus is particularly useful for measuring the tension in atravelling web such as a sheet of cellulose film where the tension mayvary at one or more points across the web due to tight or slacklongitudinal lanes in the film. Such lanes are particularly troublesomein the manufacture of cellulose film as they prevent the film from lyingflat in a transverse direction and cause creasing and other troubleswhen the film is fed to printing machines or converting machinery suchas bagmaking machines. ing drying after wet processing when the dryingapparatus is working inefiiciently.

By employing the apparatus in accordance with the invention, it ispossible to watch continuously the tension at a number of spaced pointsacross a web of cellulose film leaving a drying apparatus byindependently measuring the pressure of the gaseous medium in thegaseous cushion supporting the film at these points. Any slack or tightlanes are readily observed by comparison of the readings and appropriateadjustments can be made to the drying machine. The presence of a slacklane is indicated by a low pressure reading and a tight lane by a highpressure reading.

The apparatus according to the invention is capable of measuring thetension in any stationary or travelling web capable of being supportedby the gaseous cushion out of contact with the arcuate surface. Solidwebs such as cellulose film, films of plastic materials, paper, metallicfoil and the like are readily supported by a gaseous cushion; so alsoare semi porous webs such as bonded fibre fabrics or closely wovenmaterials when the supply of gaseous medium through the apertures in thearcuate surface is far in excess of the loss of the medium through theweb. However, the apparatus cannot be used for measuring the tension inopen mesh webs such as loosely Woven fabrics.

The web tension is measured without the web ever coming into contactwith a solid surface thus avoiding scratching of the web which oftenoccurs when conventional web tension measuring apparatus is employed.also the measurement of tension may be carried out on webs which arefreshly printed or treated with a wet coating or sizing compositionwithout the print, the coating or the sizing being smeared or otherwiseaffected.

The invention also includes a method for measuring the tension in a webwhich method comprises passing the web around an arcuate surface,maintaining the web out of contact with the arcuate surface by means ofa gaseous cushion formed by continuously supplying a gaseous mediumunder pressure to the space between the web and the arcuate surface andmeasuring the pressure of the gaseous medium within the gaseous cushionat one or more selected points.

Example perspective view of a second form of Patented Aug. 24, 1965 Theyusually appear'in the film dur- 3, '4 of holes S one millimetre indiameter" and sp one inch'apart in each row'2, 3, 4. The rota/ 2;}, 4"

are spacedone and: a half inches apart. Compressed air at arpressure ofthree poundsper square inchisi supplied to the interiorrof thetube 1 byapump 6rthrough'a snpply i pipe 7 "and on passing through the. holes 5s}1'ppor ts fa travelling cellulosefilmfi forty eight: inches in'width-on r I through an angle of 90; 7

one eighth 'of an inch in diameter, isdrille'd throughq'the; wallofj'the .tube 1 and is connected by a pipe 11 to}! manometer 12. Themanometer" 1 2' wi1l v mleasl lre the pressure of theairlin thecushion9Tadjacent the test hole, 10 and as thisfvalue is related to t-hetension in' the film 8 the manometer units of tension. r v. v -1 r J;

'In FIGURE 3, the apparatus lisfidentical with that;

series of six test-holes 10 are" provided at intervals of inches.-Eachvtest -hole 10 is connected independent-x, ly to one of sixmanometers 12 inount'ed sideby side on.

andisplay panel 1 3. .The reading oi eachi-manometer 12 will be ameasure of the tension ini'the film 8 passing- 1 12 is, for convenience,calibrated in; v

4'of holes S, and in line with the row 3, atest holerltl which the webspassed, theiarcuate surface having ap'er ha th ou h which as scpus mmca be i pp under pressure to provide asupporting gaseous cushionbetween theundersurface of the web and the. arcuatezsurface,: a'asupplymeansyfor continuously supplying the gaseous medium runderfpressure tothe apertures, the arcuate-fsurface.having at least twotesteholes spacedapart g enerally transveris ely=ofithe web for communicating with-'thegaseou's'cushi J v nected with" each itestQhple for determining ,thepressure and apressure measuring device con-n of the gaseousmedium-Jinhthewigas'eous' cushion inlthe vicinity -of I the "test-hole?1 ZLAn' apparatus as-claimed in clainfl in which ap- 1 paratustheaperturesare arranged in.at least two .rows 15 in 'a' directiontransverseto the path of the'zweb; 1 3;, An apparatusiastclaimed inclaim 1 in which apparatus the pressu1efm'asi1ring device is; ama'norneter.

""1 -4QAnapparatusfor measuring thetehsion inia web whichapparatus-comprises atubular memberv having an 2'0 shown in FIGURES land2 with the exception thatra medium=can pass frorn 'thefinterior of thetubulanmemfound thefltu'be l'at positions adjacent the test holes;

1 0 T-hu'sQas shownin FIGURE 3; the presence and position of" a slacklongitudinal band orlane'l4' in the film 8 will be'in'dicatedby alow-reading on the; cor-f responding manometer' 12 when compared with.the.

ber'to provide a supportingf'g'aseous cushion betweenthe under surfaceofthelweb and thearcuate surface, a supply means ,-for continuouslysupplying the gaseous medium under pressure to Ithe' -interior ofthetubular member,

s therrcuatesurface-"haying at least two'te stho'les spaced apartgenerally t'ranyersiely of theweb for communicating readings on theother manometers' n Similarly, a tight 1 longitudinal bandor lane in thefilm 8 will be-indicate'd by a'high reading on the correspondingrnanometer 12 and low readingson the remaining manometer-s 12 I fTheapparatusmayireadily be incor orated in-any webl handling machinery andonly requires a source of com- I pressed air for its operation. ThepresSure -ofair. 'employed must be sufiicient to support the'web outofcon-' tact with the tube but otherwise its value has, substantiallynoefiect 'upo nth'e web tension measurements, f

I claimz' nicliannjcxflounissifn gna .gamma?!'.

1. 'a param 'ns; measuring the t eris ion ina web which apparatuscomprises an arcuate sUrface around with thega'seouscushionVanda-pressure measuring device connected 'with 'eachtest hole fordetermining the pressure of the gaseous medium in jthelgaseous. cushion in the Yicinity ofithe" testholehf Refererice sCitedby. the Examiner V J osni n- 'P'. STRlZAK, DAVID SQHONBE I

1. AN APPARATUS FOR MEASURING THE TENSION IN A WEB WHICH APPARATUSCOMPRISES AN ARCUATE SURFACE AROUND WHICH THE WEB IS PASSED, THE ARCUATESURFACE HAVING OPERTURES THROUGH WHICH A GASEOUS MEDIUM CAN BE CUPPLIEDUNDER PRESSURE TO PROVIDE A SUPPORTING GASEOUS CUSHION BETWEEN THE UNDERSURFACE OF THE WEB AND THE ARCUATE SURFACE, A SUPPLY MEANS FORCONTINUOUSLY SUPPLYING THE GASEOUS MEDIUM UNDER PRESSURE TO THEAPERTURES, THE ARCUATE SURFACE HAVING AT LEAST TWO TEST-HOLES SPACEDAPART GENERALLY TRANSVERSELY OF THE WEB FOR COMMUNICATING WITH THEGASEOUS CUSHION AND A PRESSURE MEASURING DEVICE CONNECTED WITH EACHTEST-HOLE FOR DETERMINING THE PRESSURE OF THE GASEOUS MEDIUM IN THEGASEOUS CUSHION IN THE VICINITY OF THE TEST-HOLE.